Conventionally, recording electrocardiograms has been generally adopted as a technique to diagnose heart diseases.
However, conventional electrocardiography is insufficient for example to determine the location, size and geometry of a part to be treated in a heart surgery and it cannot satisfactorily locate an affected part.
This is attributed to the fact that electrocardiography is an indirect measurement methodology. Different subjects have different tissues existing between their hearts and body surfaces, different positional relationships between their hearts and other organs and bones, their respective hearts having different sizes, a different electric conductance for each tissue of their bodies, and the like. As such, it has been significantly difficult to accurately determine an affected part from information obtained from indirect measurement such as electrocardiography.
As such an indirect measurement methodology is disadvantageous, as described above, a method has been adopted to more directly identify the location of an affected part.
For example, thoracotomy is employed to expose a heart and a needle electrode is directly stabbed in the heart or a meshed electrode is brought into contact with the heart to measure myocardial potential at multiple points simultaneously to precisely locate an affected part. Thoracotomy, however, is a significant burden on patients. In addition, the multi-point, simultaneous, myocardial potential measurement and its data analysis effected in thoracotomy to identify the location of an affected part require a long period of time and thus prolong thoracotomy disadvantageously.
Accordingly there is a strong demand for a method capable of locating an affected part in a short period of time with high precision.
Another direct approach has also been adopted in recent years. It uses a catheter to conduct diagnosis and provide treatment. More specifically, a tip provided catheter having an electrode and a heater is inserted to intracardiac cavity and chest x-ray fluoroscopy is provided, while an electrophysiological test is conducted to locate an affected part and a methodology referred to as high frequency catheter cauterization is also employed to rapidly ablate a targeted site to rapidly treat the site.
In this approach, however, the electrophysiological test requires a period of time and chest x-ray fluoroscopy exposes doctors and radiographers to large doses of x-ray radiation.
It has been known that of various heart diseases, atrial flutter and atrial fibrillation are caused by an abnormal excitation propagation circuit formed in a heart muscle. More specifically, atrial flutter is caused by an abnormal, electrical reentry circuit, referred to as a macro reentry circuit, formed in a vicinity of a tricuspid annulus and atrial fibrillation is caused by an abnormal, electrical reentry circuit, referred to as a micro reentry circuit, formed in an atrium in large numbers (multiple wavelength theory). From a recent study it has been known that an early stage of paroxysmal atrial fibrillation would be induced by firing at a focus of a pulmonary vein.
To treat atrial flutter and fibrillation it is important to identify these reentry circuits and a firing site at a focus of a pulmonary vein. However, indirect measurement using electrocardiography, as described above, would hardly provide precise identification, and a myocardial potential measurement in thoracotomy and an electrophysiological test using a catheter or any other similar direct tests are a significant burden on patients and doctors.
Accordingly there is a strong demand for non-invasively diagnosing these reentry circuits and a firing part at a focus of a pulmonary vein.
In a variety of fields a superconducting quantum interference device (SQUID) magnetometer has been applied. It uses an SQUID capable of detecting with high sensitivity a magnetic flux of one billionth of geomagnetic field. In particular, in the field of somatometry, which strongly demands non-invasive measurement, as described above, an attempt is being made to use a SQUID magnetometer to provide a non-contact magnetic field measurement of human bodies.
In particular, the development of thin-film device fabrication technology in recent years has allowed the development of a DC-SQUID, and an attempt is being made to use a SQUID magnetometer to measure a magnetocardiogram, a distribution of a magnetic field of a heart.
However, a magnetocardiogram alone cannot directly display the location, size and geometry of an affected part in a human body and would hardly let a doctor know a correct, relative positional relationship of an electrical reentry circuit in a heart.
Accordingly it has been proposed that in diagnosing atrial flutter and fibrillation, the location of an abnormal, intramyocardial excitation propagation circuit causing atrial flutter and fibrillation is identified by visualizing an intramyocardial, electric current behavior from a magnetocardiographic distribution represented in a magnetocardiogram. One such approach adopted is to use one or more current dipoles to mimic the source of a magnetic field for visualization. If a large number of micro reentry circuits exist, however, the number of the circuits and their respective locations cannot accurately be identified. Furthermore in such an approach a result of mimicking the source of a magnetic filed would disadvantageously depend on an initial value that is set.
Accordingly the present invention contemplates a magnetocardiographic diagnosis apparatus for diagnosis of atrial flutter and fibrillation and a method of identifying the electrical reentry circuit, capable of employing non-invasive magnetic field measurement to obtain data representative of a three-dimensional, intramyocardial electrical behavior used to identify a positional relationship of an abnormal, intramyocardial electrical reentry circuit safely, rapidly and with high precision.